Thread: D2: Throttle use causes Fuse 25 (Brake/Reverse Lights) to blow

G'day all,

For several weeks I've been unable to keep my Brake/Reversing lights operating for any length of time. Fuse 25 (15A) keeps blowing.

I'd replace the fuse, check that all lights were working OK and then go for a drive. By the time I'd get back, the fuse has blown again.

Today, I decided to get to the bottom of it.

Reading about other peoples' experiences, I checked all the globes and found that someone, could have been me, replaced a 21W fog lamp with a Stop/Tail globe. Aha! That's it! .... No, that wasn't it.

I read about brake pedal switches so, having one handy, I tried replacing that. No, that wasn't it either.

Then I decided to get all scientific about it and wired an ammeter (DMM) in series with the fuse. This opened up a whole can of worms!

New fuse, engine on, tried the Reverse lights.... 3.3A, no problem. Brake lights on, 5.4A... no problem. Brake lights and Reverse lights together?.... No problem, 8.xA. Looking good!

Then I decided to go for a spin around the block, hoping the ammeter would show when the fuse blows so I could associate whatever was happening with the moment the fuse blows.

I didn't have to go far. As soon as I hit the throttle to reverse out the driveway, the fuse blew.

I'm stumped. I've looked at the circuits and the only relationship I can find between Fuse 25 and the throttle is in relation to Cruise Control. But the Cruise Control has been off the whole time.

UPDATE

Further investigation shows that the fuse only blows when the vehicle is in reverse gear and the throttle is pressed. In reverse gear, with no throttle, no impact on the fuse. Driving forward with/without brakes on has no effect on the fuse.

UPDATE 2

Getting a bit more nuanced now. New fuse, in reverse gear, very slowly on the throttle all the way up to about 1200rpm.... no problem. Tiny blip on the throttle.... game over. It's as if a small amount of torque on the engine and, by extension, the drivetrain, causes something to short. Maybe a reverse light switch? XYZ switch? Something else? I think I've gone as far as I can. Time to call in the troops.

Has anyone seen this before? Can anyone offer any clues?

Thanks,

Mark

Hi Mark, please check and tell details:

- what globe/W of your brake and reverse lights are? is that genuine or generic?
- is there any extra accessories for the reverse (extra lights, extra aftermarket reverse parking sensors...)
- is there any LED lights for reverse or some extra LED lights around the car (spot lights)?